Blood-sucking flies can be used as 'flying syringes' to detect infectious disease in animals before they spread to humans.

Researchers analyzed the blood meals of flies that suck blood from animals to find out which types of animals are carrying specific diseases.

The research could help control future outbreaks of diseases such as Ebola and Zika, which are infectious diseases in animals that can be transmitted to humans.

Researchers analyzed the blood meals of flies that suck blood from animals to find out which types of animals are carrying specific diseases. Pictured is the tsetse fly, a type of fly that the researchers analyzed in their study

According to the researchers, seven new pathogens are identified worldwide each year, and this is predicted to reach 15-20 every year by 2020 because of increased human contact with wildlife species that potentially carry disease.

But despite scientific advances, researchers still can't predict exactly where, when and how epidemics arise.

'This is a huge public health issue that urgently requires new tools for the active monitoring of outbreaks and rapid diagnosis of the pathogens involved,' said senior author of the study and evolutionary geneticist Dr Franck Prugnolle, from the National Center for Scientific Research (CNRS) in Montpellier, France.

'We wanted to investigate whether blood-feeding insects could act as a sampling tool out in the wild environment, allowing us to monitor the presence and emergence of infectious disease.'

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Normally, to study pathogens that are circulating in wild habitats, researchers analyze animals caught for food by humans.

However, these animal's usually only represent a fraction of a region's wildlife.

Another method is to trap animals to study for the presence of infection in their organs and tissues, but this isn't easy to do and it's dangerous to protected species.

Previous research has shown that the DNA of animals, and from diseases such as malaria, is preserved in the blood meals of flies.

This gave Dr Prugnolle and his team the idea to see whether blood meals could be used as a non-invasive way of studying the pathogens circulating in wild animals.

First author of the study Dr Paul-Yannick Bitome-Essono collectting trapped blood-feeding flies from a Vavoua trap in Moukalaba-Doudou National Park, Gabon

So the researchers conducted a study over a 16-week period in four national parks in the forests of Gabon, Central Africa.

They set up traps for three types of flies (tsetse flied, stomoxids and tabanids) and then analyzed the insects' blood meals to determine the origin of the blood and the types of malaria parasites present.

They captured more than 4,000 flies - of which 30 per cent, mostly tsetse flies, were engorged with blood.

'We thought the tsetse fly might be a good candidate in our study, as both sexes feed on blood, they are large and easily trapped, present in large numbers in Central Africa, and are opportunistic feeders with no strong preference for a particular host animal, so would feed on a large range of wildlife, said lead author of the study Dr Paul-Yannick Bitome-Essono, from the CNRS in France.

Infographic showing how Ebola spread. Ebola is a zoonotic disease, meaning it a disease, which means its spread between animals and people. When humans contract the virus, they can then spread it between each other

The researchers used a new technique for studying the blood meal DNA, finding the host animal origin for three-quarters of the samples.

The results revealed that flies had fed on over 20 different species ranging from elephants and hippopotamuses to reptiles and birds.

They found malaria parasites in nearly 9 per cent of the blood meals, including 18 cases of previously undocumented malaria species.

They also identified the animal hosts of some malaria species whose preferred host was not previously known.

'These results show that blood meals of the engorged flies can be successfully used to analyse the diversity of known malaria parasites,' said Dr Prugnolle.

He said the the next step is to look at ways to improve the method with new techniques for DNA sequencing and pathogen detection methods.

'This approach of 'xenosurveillance' could detect pathogens before they spread to humans, as well as the emergence of new diseases in wild animals that may threaten their long-term survival,' said Dr Prugnolle.

WHAT IS SLEEPING SICKNESS?

This disease is transmitted by the bite of an infected tsetse fly.

The World Health Organization (WHO) estimates that nearly 450,000 cases occur each year, and instances of infection have been discovered in the more popular spots for tourists such as Kenya and Tanzania.

Symptoms of the disease include fever, headaches, joint pains, and itching in the early stage, and confusion, sensory disturbances, poor coordination, and disrupted sleep cycles in the second stage.

If the disease goes untreated in its first stage, it causes irreparable neurological damage; if it goes untreated in its second stage, it is fatal.

The type of treatment depends on the stage of the disease. The drugs used in the first stage of the disease are of lower toxicity and easier to administer. The earlier the disease is identified, the better the prospect of a cure.

Treatment success in the second stage depends on a drug that can cross the blood-brain barrier to reach the parasite. Such drugs are toxic and complicated to administer.